1. Field of the Invention
The invention relates to a method for monitoring of the amount of oil flowing in an oil circulation system of an oil lubricated vacuum pump, having an oil filter and an oil cooler, wherein the oil cooler is a heat exchanger having the oil and a cooling fluid flowing through it. The invention also relates to an oil-lubricated vacuum pump for operation in accordance with this method.
2. Discussion of Related Art
In general oil lubricated vacuum pumps, such as vane-type rotary pumps, rotary plunger vacuum pumps, have an oil filter in the oil circulation system. Among other things this filter removes from the oil all solid particles which can impair the functioning of the pump so that, in time, the filter becomes plugged with the solid particles and the amount of oil flowing through the filter decreases. If the filter is not replaced, the amount of oil passing through the filter can gradually be reduced until the oil no longer functions properly to cool, seal and lubricate the pump. This condition risks overheating the pump and scoring the piston. The present invention relates to the problem of providing a control system for determining when to replace the oil filter.
An attempt has been made to determine whether or not sufficient oil is circulating in an oil lubricated vacuum pump solely by the temperature of the oil. However, solely temperature-based control has proven to be insufficient, since the temperature of the oil is also affected by suction pressure, the temperature of the environment and the temperature of the pumped medium. Therefore no exact determination of the amount of oil flowing in the oil circulating system can be based solely on the temperature of the oil.
An attempt has also been made to use the difference in the pressure in front and behind the oil filter, but this pressure difference also depends on suction pressure, especially in the case of vacuum pumps having no oil feed pump. Thus, merely determining the pressure difference does not provide a determination of the amount of oil flowing through the filter. Moreover, this measurement does not take into account the viscosity and the temperature of the oil, which are important to the determination.